1. Field of the Invention
The present invention relates to a device and a method for displaying an image, and particularly relates to control of a scan mirror.
2. Description of the Background Art
As to an image display device, Japanese Patent Laying-Open No. 2006-323035, for example, discloses a technique for “controlling display of an image with higher precision and higher accuracy, and achieving a display device at a lower price” (“Problems to be Solved” in “Abstract”).
Japanese Patent National Publication No. 11-514781 discloses an invention relating to “a scanning device having a scanning element and a control system for controlling a position of the scanning element, in which a non-scanning plane of the scanning element configures a measurement reference plane, the control system has a position detection system for detecting a position of the scanning element, and an output terminal of the position detection system is connected to a control circuit for correcting the position of the scanning element in a direction vertical to the reference plane” (the first paragraph on page 5 in the specification).
Japanese Patent Laying-Open No. 06-342126 discloses “a projection display device, more specifically, a projection display device in which an optical signal emitted from an optical shutter array having multiple optical shutter elements arranged in a one-dimensional manner, based on an image data, is scanned with a deflection mirror to project a two-dimensional image” (paragraph 0001).
Japanese Patent National Publication No. 08-505717 discloses an invention relating to “a method of compensating for a pyramidal error (Pyramidalfehlerausgleich) caused by an insufficient tilt of mirror surfaces of a rotary polygon mirror acted upon by a light beam and deflecting a bundle of rays, in which when the mirror surfaces have a tilt error, deflection correction (Korrekturablenkung) of the bundle of rays reflected from each of the mirror surfaces is conducted at a correction angle in a direction opposite to the direction of the deflection caused by the insufficient tilt”, and an invention relating to “a device for implementing the above-described method, including: a rotary polygon mirror acted upon by a light beam so as to deflect a bundle of rays by means of its mirror surfaces; a deflector for conducting, when the mirror surfaces have an insufficient tilt, deflection correction of the bundle of rays at a correction angle in a direction opposite to the direction of the deflection caused by the insufficient tilt; and a control device for controlling the deflector so as to correct the deflection” (the first paragraph in the specification).
Japanese Patent Laying-Open No. 2001-056444 discloses an invention relating to “a laser display device for driving each of R, G, and B lasers based on a video signal, and scanning a laser beam of each of the lasers on a color monitor in a horizontal direction and a vertical direction by means of horizontally-scanning means and vertically-scanning means to display an image” (paragraph 0001).
In a beam-scanning display device such as a laser projector, drive sensitivity of a scan mirror may differ from ideal sensitivity predefined as design information, because of an individual difference in the scan mirror. Here, the drive sensitivity refers to a ratio of an output (e.g. a moving amount of the scan mirror, such as a scan angle) to an input (e.g. a voltage value) provided to a drive mechanism of the scan mirror. For example, in the case that the drive sensitivity of the scan mirror in a vertical direction is higher than ideal sensitivity, the scan mirror is moved in the vertical direction by an amount equal to or larger than a designed amount, in response to the same input, so that an interval between spots of a laser beam reflected by the scan mirror is increased. Consequently, conspicuous scan lines inevitably appear in a projected image.
On the other hand, in the case that the drive sensitivity is lower than ideal sensitivity, a moving amount of the scan mirror is smaller than a designed amount, so that an interval between spots of a laser beam reflected by the scan mirror is decreased, resulting in that an image is projected in an overlapping manner. Accordingly, there is a demand to achieve an ability to prevent deterioration in quality of the projected image.